What is the recommended treatment for a urinary tract infection caused by Streptococcus agalactiae (Group B Streptococcus) in an otherwise healthy adult?

Treatment of Streptococcus agalactiae (Group B Streptococcus) UTI in Non-Pregnant Adults

Amoxicillin 500 mg orally every 8 hours for 7-10 days is the recommended first-line treatment for uncomplicated UTI caused by Group B Streptococcus in otherwise healthy non-pregnant adults. 1, 2

Primary Treatment Options

For uncomplicated lower UTI:

• Amoxicillin 500 mg PO every 8 hours is the preferred agent 1, 2
• Amoxicillin-clavulanate is an alternative first-choice option, particularly useful in liquid formulation for patients unable to swallow tablets 1
• Penicillin G 500 mg orally every 6-8 hours is recommended as the preferred agent due to its narrow spectrum of activity 2
• Ampicillin 500 mg orally every 8 hours is an acceptable alternative to penicillin 2
• Treatment duration should be 7-10 days for standard cases 2

All GBS strains demonstrate high susceptibility (>95%) to ampicillin, amoxicillin-clavulanate, and 100% susceptibility to rifampicin 3. More recent data confirms all GBS strains remain sensitive to penicillin, ampicillin, and vancomycin 4.

Penicillin-Allergic Patients

For patients with penicillin allergy:

• Clindamycin 300-450 mg orally every 8 hours is recommended 2
• Susceptibility testing must be performed before using clindamycin due to increasing resistance rates (13-25% resistance documented) 4
• Vancomycin remains an option if clindamycin resistance is present 4

Complicated UTI or Severe Presentations

For complicated infections or systemic symptoms:

• Initial IV therapy with ampicillin 2 g IV every 4-6 hours, then transition to oral therapy once clinically stable 2
• Combination therapy with ampicillin plus an aminoglycoside for severe presentations 2
• Extend treatment duration to 14 days for complicated infections or when prostatitis cannot be excluded in men 2

Critical Clinical Distinctions

Asymptomatic bacteriuria in non-pregnant patients:

• No antibiotic treatment is indicated if the patient is asymptomatic with GBS isolated from urine culture and normal urinalysis 2
• This represents asymptomatic bacteriuria that should not be treated according to IDSA guidelines 2
• Treatment is only appropriate if the patient has symptomatic UTI, abnormal urinalysis, or underlying urinary tract abnormalities 2

The management of GBS bacteriuria is fundamentally different between pregnant and non-pregnant patients - all GBS bacteriuria requires treatment in pregnancy due to neonatal disease risk, but non-pregnant adults should only be treated if symptomatic 2

Important Diagnostic Considerations

Before initiating therapy:

• Obtain urine culture with susceptibility testing when possible 1
• Identify potential reservoirs of infection including vagina, urethra, and gastrointestinal tract, as the vagina is a potential GBS colonization site in females 1, 3
• Thorough examination to identify infection foci outside the urinary system is essential for successful treatment 3

Monitoring and Follow-up

Post-treatment surveillance:

• Follow-up urine culture after treatment completion may be warranted to ensure eradication, especially in patients with recurrent UTIs 2
• This is particularly important given that GBS can persist in reservoirs and cause reinfection 3

Common Pitfalls to Avoid

• Do not treat asymptomatic bacteriuria in non-pregnant patients - this leads to unnecessary antibiotic exposure, resistance development, and potential adverse effects without clinical benefit 2
• Do not apply pregnancy treatment guidelines to non-pregnant patients - the CDC guidelines for universal treatment of any concentration of GBS in urine apply specifically to pregnant women 2
• Always perform susceptibility testing before using clindamycin due to documented resistance rates of 13-25% 4
• Consider local treatment with vaginal lavages in addition to systemic antibiotics when vaginal colonization is identified 3